Developing apparatus for photocopy machines

ABSTRACT

A developing apparatus for diazo-type photocopy machines, which is adapted to prevent external leakage of gaseous ammonia developing medium to the surrounding environment is provided. The apparatus comprises a developing chamber having transport means for advancing exposed diazo-type sensitized paper therethrough, means for introducing and circulating gaseous ammonia within the chamber to develop an image on the sensitized paper; and a vacuum pump for evacuating said ammonia from the developing chamber. The vacuum pump is adapted to remove a greater volume of ammonia from the developing chamber than is introduced therein, so as to maintain the internal pressure of such chamber at below atmospheric, and thereby prevent external leakage of ammonia fumes. As an additional feature of the invention, vacuum surge means are provided to maintain the below atmospheric pressure within the developing chamber at a relatively constant level to ensure uniform development of the sensitized paper.

[ 51 Aug. 19, 1975 United States Patent n 1 Bennett et al.

[57] ABSTRACT A developing apparatus for diazo-type photocopy mal l DEVELOPING APPARATUS FOR PHOTOCOPY MACHINES chines, which is adapted to prevent external leakage of gaseous ammonia developing medium to the surrounding environment is provided. The apparatus comprises a developing chamber having transport means for advancing exposed diazo-type sensitized paper therethroughfmeans for introducing and circulating gaseous ammonia within the chamber to develop an image on the sensitized paper; and a vacuum pump for evacuating said ammonia from the developing chamber. The vacuum pump is adapted to remove a greater volume of ammonia from the developing chamber than is introduced therein, so as to maintain 70 W Y EN .5 1 .m N 5 a 3w.) .u v 0 0 0 ii mm w M m6 0.. m 7 saw m r l m.

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and thereby prevent external leakage of ammonia fumes. As an additional feature of the inven tion, vacuum surge means are provided to maintain the below atmospheric pressure within the developing [56] References Cited UNITED STATES PATENTS chamber at a relatively constant level to ensure uni x form development of sensitized paper.

Hruby Hurtig et me rl e B 0 3 777 999 NH 813 17 Claims, 3 Drawing Figures Primary E.\'uminerRichard A. Wintercorn Walter C. Kehm; Arthur Attorney, Agent, or Firm- Dresner PATENTED AUG 1 91975 [Ill/1' DEVELOPING APPARATUS FOR PHOTOCOPY MACHINES BACKGROUND OF THE INVENTION DiazJo-type photocopy machines have, since their advent, created numerous problems with regard to the venting and exhausting of ammonia gases utilized in the development process, and the contamination of the surrounding environment by ammonia fumes. Ammonia gas is normally pumped into the developing chamber of such photocopy machines under pressure in a manner such that the gas fully contacts sensitized paper being transported therethrough to develop an image thereon. The sensitized paper enters and leaves the developing chamber by means of one or more openings provided for such purpose, and, unfortunately, the pressurized ammonia gas in the chamber has a tendancy to leak into the surrounding atmosphere through such openings. in an attempt to minimize such leakage photocopy machines of this type have been provided with one or more pairs of resilient rollers disposed adjacent the openings in the chamber, and defining relatively narrow nips through which the sensitized paper may pass. While such rollers tend to reduce some of the leakage of ammonia into the surrounding atmosphere, they, of course, cannot completely prevent such leakage, since the ammonia in the chamber is pressurized above the pressure of the surrounding ambient atmosphere, and the differential pressure thereby established across the rollers causes ammonia fumes to flow exterior of the chamber through the nip between the rollers.

To deal with this problem, rather than solving it, the noxious effect of the ammonia fumes which leak into the area surrounding the photocopy machine is minimized by providing large exhaust fans in the immediate vicinity of the machine. Such fans require extensive duct work associated therewith, so that the fumes may be exhausted to an area outside of the building in which the machine is located. This, of course, greatly increases the cost of installing and operating such a machine. in addition, photocopy machines of this type have themselves been provided with exhaust fans located in the housing which encompasses the developing chamber. Such fans also reduce the amount of ammohia fumes leaked into the surrounding area, but do not completely eliminate such fumes. Moreover, the internal exhaust fans must also be provided with extensive duct work to carry the ammonia fumes to the exterior of the building, again adding to the cost of installation, maintenance and operation of the machine.

There have been many recent improvements to phomopy machines of the type described above, which relate to the disposal of gaseous ammonia utilized in such machines, but such improvements are generally directed toward the neutralization of ammonia after discharge from the developing chamber by absorption through the means of a suitable absorbent material, or the breakdown of the ammonia gas into its nontoxic component parts of gaseous nitrogen and water vapor by means of a catalytic converter. However, the foregoing devices for neutralizing ammonia are disposed downstream of any internal exhaust fan, and, accordingly, such devices do not prevent leakage from the developing chamber, but merely deal with the portion of ammonia that is discharged from the machine by the exhaust fan. US. Pat. No. 3,467,491 discloses a device be utilized with any other type for the catalytic treatment of vented gases containing ammonia, and shows a typical arrangement of devices this type utilized to neutralize ammonia fumes. It can be seen from such patent that the disclosed system deals merely with the disposal of the ammonia that is drawn from a diazo printing machine, rather than prevention of ammonia leakage from the developing chamber of such machine.

SUMMARY OF THE lNVENTlON In accordance with the present invention an improved developing apparatus for photocopy machines of the type described hereinabove is provided to overcome the problem of developing medium leakage to the exterior of such machines, by completely and fully preventing all such external leakage. This is accomplished by means of a developing chamber which is adapted to operate at a pressure below that of the surrounding atmosphere, so that a differential pressure is developed across the chamber which tends to draw ambient air into the chamber, rather than discharging fumes of developing medium to the exterior of such chamber. It has been found that the operation of a developing chamber at sub-atmospheric pressures does not in any way impair the development process, of sen sitized paper, but does, indeed, prevent and eliminate the problem of developing medium leakage which was heretofore quite prevalent.

In general, the developing apparatus of the present invention comprises, in combination, a developing chamber having an inlet for receiving liquid or gaseous developing medium, an outlet for discharging such developing medium, and means for transporting sensitized paper therethrough in the line of flow from the inlet to the outlet; means for introducing liquid or gaseous developing medium into the developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove the developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of liquid or gaseous developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium.

It should be noted at this juncture that the developing apparatus of the present invention is primarily intended for use in diam-type photocopy machines, wherein the developing medium is anhydrous or aqueous ammonia, and accordingly, for the purposes of describing and illustrating the present invention, the developing me dium will be referred to hereinafter as ammonia. However, it will be appreciated by those skilled in the art that the basic concept of the present invention, that is, a sub-atmospheric developing chamber, could likewise of developing medium.

The developing chamber can be constructed in any desired configuration well known in the photocopy machine art. Such configurations include a straightthrough or elongated chamber, in which sensitized paper to be developed is transported along a straight line path by means of a series of cooperating rollers. Chambers formed in this configuration have an inlet for the sensitized paper at one end, defined by a pair of such rollers having a nip therebetween through which the sensitized paper passes, and a corresponding outlet at the other end of the chamber, similarly defined by a pair of rollers having a nip therebetween through which the paper passes. The developing chamber can also be of the circular path type, wherein a rotatable cylindrical drum having a fixed perforated sleeve mounted therearound is disposed within an enclosed chamber having a single opening for both the entrance and exit of the sensitized paper. In this configuration sensitized paper is transported into the opening by means of a series of cooperating rollers, and is then advanced in a circular path through the developing chamber by means of the rotatable drum via an annular space defined by the drum and the sleeve. A doctor blade provided adjacent said drum separates the developed sensitized paper therefrom, and permits its exit via the same opening through which it entered.

Although either of the above described developing chamber configurations could be utilized in the present invention, it should be noted that the latter type having the cylindrical drum is preferred, since the single opening for the entrance and exit of the sensitized paper minimizes the internal leakage of air into the chamber, and thus prevents undue dilution of the ammonia within the chamber. In this manner, a reduced volume of ammonia may be utilized for the development process.

The means for introducing ammonia into the developing chamber is preferably a circulating system comprising a closed reservoir containing the ammonia, and a pump for circulating the ammonia between the reservoir and the developing chamber. The reservoir includes an outlet connected directly to the inlet of the developing chamber to feed ammonia therein, and an inlet connected to the positive pressure side of the pump. The negative pressure or suction side of the pump is connected to a second outlet provided in the developing chamber. It should be noted that the ammonia circulating pump is preferably separate and apart from the vacuum pump referred to hereinabove, and that each pump is connected at its suction side to a different outlet from the developing chamber. However, it should also be noted that both pumps can be driven by a single electric motor common to both.

In the preferred embodiment, the developing medium is anhydrous ammonia and the reservoir contains a solution of aqueous ammonia and gaseous anhydrous ammonia disposed thereabove. The positive pressure side of the ammonia circulating pump is in communication with the reservoir at a point below the surface of the aqueous ammonia, so that gaseous ammonia, to gether with any air drawn into the developing chamber, is bubbled through the aqueous ammonia to facilitate its dissolution, and thereby generate additional quantities of gaseous anhydrous ammonia. In addition, the reservoir outlet is disposed at or adjacent the top thereby and the pressurized mixture of air and anhydrous ammonia entering the reservoir raises the internal pressure within the reservoir a sufficient amount to pump the anhydrous ammonia from the top of the reservoir above the aqueous ammonia into the developing chamber.

As an additional feature of the invention, vacuum surge means are provided to maintain a relatively constant below atmospheric pressure within the developing chamber. In the preferred embodiment, such means comprises a vacuum surge chamber disposed in the line of flow from the primary outlet of the developing chamber to the suction side of the vacuum pump, and

consists of a sealed cylindrical tank having an inlet in communication with the outlet of the developing chamber, an oulet in communication with the suction side of the vacuum pump, and a normally closed control valve communicating the interior and the exterior of the tank. The valve is responsive to the below atmospheric internal pressure of said tank to open when such internal pressure is reduced below a predetermined value, thereby permitting the entry of ambient air to modulate and maintain the internal pressure of the tank at the desired level.

As an alternative, the vacuum surge means can comprise simply a normally closed pressure sensitive control valve disposed in a wall of the developing chamber and communicating the interior thereof and the surrounding ambient atrnosphere. Such valve operates in the same manner as the control valve utilized in the surge chamber and serves to maintain the below atmospheric pressure within the developing chamber at the desired level.

It has been found under test conditions that a subatmospheric pressure in the range of about 0.2 inches of water column to about 1.0 inches of water column yields extremely good results in both the prevention of external leakage from the developing chamber and the maintenence of good quality photocopy prints. However, in this regard it has also been found that the use of the vacuum surge chamber, as described above, yields better results in maintaining the sub-atmospheric pressure of the developing chamber, than merely the use of a control valve directly in the developing chamher.

The gaseous ammonia exhausted from the developing chamber and/or the vacuum surge chamber by the vacuum pump can be vented to the exterior of the building in which the photocopy machine is utilized in a conventional manner by means of suitable duct work, or in the alternative, can be neutralized by passing such ammonia through a suitable liquid absorbent material, such as citric acid. For such purpose, an absorption vessel containing the absorbent material is formed as part of the photocopy machine and suitable tubing is provided from the vacuum pump to such reservoir, in a manner such that the ammonia may be bubbled through the absorbent to accomplish complete neutralization thereof. As a still further alternative, the outlet of the vacuum pump can be connected to a catalytic converter for the breakdown of the ammonia to its component constituents of nitrogen gas and water vapor. The foregoing features of the developing apparatus of the present invention is further described with reference to the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a rear perspective view of a photocopying machine embodying the developing apparatus of the invention;

FIG. 2 is a schematic diagram of a preferred embodiment of the developing apparation of the invention; and

FIG. 3 is a cross-sectional view of the vacuum surge chamber shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. I, a diazo-type photocopy machine l is provided with a sub-atmospheric developing apparatus in accordance with the invention. Such developing apparatus comprises a developing chamber 2 having an inlet 3 for receiving gaseous ammonia, a first outlet 4 and a second outlet 5, both adapted to discharge a mixture of ammonia and air therefrom. As shown schematically in FIG. 2, developing chamber 2 includes a rotatable cylindrical drum 6 for transporting sensitized diazo-type paper material 42 therethrough in a manner such that the paper is contacted by the ammonia introduced into the developing chamber to develop the latent image thereon. A fixed perforated cylindrical sleeve 7 is disposed in a spaced apart position around drum 6 to define an annular space for the paper and guide the same through the developing chamber. The perforations in sleeve 7 permit the ammonia developing medium to fully contact the sensitized paper during the development process.

A reservoir 8 containing a solution of aqueous ammonia 9 and gaseous anhydrous ammonia 10 disposed above such aqueous ammonia is mounted at the rear of photocopy machine 1. Reservoir 8 includes an outlet 11 at the top thereof connected to inlet 3 of the developing chamber by means of flexible tubing 12, and an inlet 13 having a tubular portion 14 extending into the reservoir to a point below the surface of the aqueous ammonia 9. Outlet 5 of the developing chamber 2 is connected by means of flexible tubing 15 to the suction side of a piston pump 17 via pump inlet 16, and the pressure outlet 18 of pump 17 is connected by means of flexible tubing 19 to the inlet 13 of reservoir 8. In this manner, gaseous anhydrous ammonia is circulated by means of pump 17 to and from reservoir 8 via developing chamber 2. Since tubular extension 14 communicates with reservoir 8 at a point below the surface of the aqueous ammonia 9, the gaseous ammonia, together with any air drawn into the system, which is pumped from the developing chamber 2 by means of pump I7 is bubbled through such aqueous ammonia. This serves to facilitate the dissolution of the aqueous ammonia to generate additional quantities of anhydrous ammonia to be circulated through the developing chamber, and in addition, pressurizes reservoir 8 to a sufficient degree above that of the developing chamber, so that, due to the differential pressure between the reservoir 8 and the developing chamber 2, the anhydrous ammonia 10 disposed above the aqueous ammonia within the reservoir 8 will flow into developing chamber 2.

The outlet 4 of developing chamber 2 is connected by means of flexible tubing 20 to the inlet 21 of a vacuum surge chamber 22. An outlet 23 of the surge chamber 22 is in turn connected by means of flexible tubing 24 to the suction side inlet 25 of a piston type vacuum pump 26. It should be noted at this point that both pumps 17 and 26 are operatively driven by means of a single electric drive motor 27. Motor 27 has a drive shaft 28, which includes a pair of eccentrically driven piston rods 29 and 30, which rods are connected to pumps 17 and and 26, respectively. It should also be noted that vacuum pump 26 is capable of pumping a greater volume of gas out of the developing chamber than is circulated by pump 17. The outlet 31 of vacuum pump 26 is connected via flexible tubing 32 to a perforated gas distributor 33, which is disposed within an open top absorption vessel 34 and below the surface of a citric acid solution 35 in such vessel for the absorption of ammonia gas discharged by pump 26.

The vacuum surge chamber 22 includes a normally closed control valve 36 mounted on the bottom thereof and in communication with the exterior ambient atmosphere. As shown in FIG. 3, control valve 36 comprises a flexible springlike plate 37 fixedly attached to the base member 38 of vacuum chamber 22 by means of a pair of screws 39. Base number 38 includes a circular opening 40 communicating the interior of chamber 22 and the exterior thereof, and a resilient disc 41 formed of rubber material or the like is fixedly attached to the bottom of plate 37 and is biased by such plate into a position to fully cover and seal opening 40.

In operation, a sheet of sensitized diazo-type paper material 42 is fed by suitable rollers into developing chamber 2 via opening 43 fonned in one side thereof, and is transported in a circular path through developing chamber 2 by means of rotatable drum 6. Simultaneously with the entry of the sensitized paper 42 into the developing chamber 2, pump drive motor 27 is activated to commence the flow of ammonia gas into the developing chamber 2 for the development of the latent image contained on sensitized paper 42. Upon the actuation of motor 27, pump 17 raises the internal pressure of reservoir 8 to commence the circulation of anhydrous ammonia 10 through the developing chamber 2. A portion of such ammonia, together with any air which may be drawn into developing chamber 2 via paper opening 43 is discharged via the pressure side of pump 17 to reservoir 8.

Concurrently with this operation, pump 26 draws the ammonia-air mixture from developing chamber 2 through vacuum surge chamber 22 into the pump, and discharges such ammonia-air mixture via distributor 32 into the citric acid absorption solution contained in absorption vessel 34. As noted above, the pumping capacity of pump 26 is such that a greater volume of the ammonia-air mixture contained in developing chamber 2 is removed from such chamber by pump 26 then is introduced into such chamber by pump 17, although both pumps preferably have the same pumping capacity. A greater volume of gas is removed from the developing chamber by pump 26 than is introduced therein by pump 17, since pump 17 merely circulates the gas through a closed system having a relatively constant gaseous volume. Pump 26 is adapted to remove a portion of the circulated gas as well as a portion of any air that might leak into the developing chamber. In this manner, the internal pressure of the developing chamber 2 is maintained at a level which is below atmospheric, and, thus, avoids any external leakage of ammonia fumes through opening 43. On the contrary, since the pressure within developing chamber 2 is maintained at sub-atmospheric there is a tendency for air to leak into such chamber, rather than ammonia fumes being discharged into the surrounding atmosphere.

Vacuum surge chamber 22 and control valve 36 are operative to maintain the sub-atmospheric internal pressure within developing chamber 2 at a predetermined level, preferably between about 0.2 inches and about 1.0 inches of water column. If the pressure within the developing tank is reduced below such level, the differential pressure of across control valve 36 is sufficient to overcome the biasing force of plate 37, so that disc 41 is lifted from opening 40 of surge chamber 22 to pennit the entry therein of ambient atmospheric air to once again raise the sub-atmospheric internal pressure to the desired level, whereupon the biasing force of plate 37 overcomes the differential pressure and causes disc 41 to again sealably close opening 40.

It will be apparent to those skilled in the art that vacuum surge chamber 22 may be eliminated, and that control valve 36 or a similar valve installed directly in the developing chamber 2 in communication with the exterior thereof. In such instance, the control valve operates to directly maintain the required internal pressure within the developing chamber. However, as noted hereinabove, superior results have been achieved by utilizing a vacuum surge chamber having the control valve.

The foregoing description is intended to be merely illustrative of the developing apparatus of the present invention. Other embodiments and alternative designs within the scope of this invention will be apparent to those skilled in the art.

What is claimed is:

1. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the oulet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium.

2. A developing apparatus in accordance with claim 1, in which the developing chamber includes a second outlet; and said means for introducing developing medium comprises a reservoir containing developing medium; means communicating said reservoir and the inlet of the developing chamber; and a pump connected at its suction side to the second outlet of the developing chamber and connected at its output side to the reservoir to circulate developing medium between the reservoir and the developing chamber.

3. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, and a pressure sensitive control means disposed in the developing chamber and responsive to the below atmosphere internal pressure thereof to permit the entry of ambient air when such internal pressure is reduced below a predetermined value.

4. A developing chamber in accordance with claim 3, in which said pressure sensitive means is a normally closed control valve communicating the interior and exterior of the developing chamber.

5. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, and a vacuum surge chamber disposed in the line of How from the outlet of the developing chamber to the inlet of the vacuum pump adapted to maintain a constant below atmosphere pressure within the developing chamber.

6. A developing apparatus in accordance with claim 5, in which the vacuum surge chamber comprises a sealed tank having an inlet in communication with the outlet of the developing chamber; an outlet in communication with the suction side of said vacuum pump; and a normally closed control valve communicating the interior and exterior of the tank, and responsive to the below atmospheric internal pressure of said tank to open when such internal pressure is reached below a predetermined valve to permit the entry of ambient air therein.

7. A developing apparatus in accordance with claim 6, in which the vacuum surge chamber maintains the below atmosphere pressure within the developing chamber at about 0.2 inches of water column to about 1.0 inches of water column.

8. A developing apparatus in accordance with claim 1, in which the output of the vacuum pump is in communication with an absorption vessel containing suitable material to absorb the discharged developing medium.

9. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, the output of the vacuum pump being in communication with a catalytic reactor to breakdown the discharged developing medium into its non-toxic components for exhausting into the surrounding atmosphere.

10. A developing apparatus in accordance with claim 8, in which the developing medium is anhydrous ammonia and the absorption material is citric acid.

1 l. A developing apparatus in accordance with claim 9, in which the developing medium is anhydrous ammonia and the catalytic reactor breaks down such ammonia into nitrogen gas and water vapor.

12. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, said developing chamber including a second outlet; and said means for introducing developing medium comprising a reservoir containing developing medium; means communicating said reservoir and the inlet of the developing chamber; and a pump connected at its suction side to the second outlet of the developing chamber and connected at its output side to the reservoir to circulate developing medium between the reservoir and the developing chamber, said developing medium being anhydrous ammonia; the reservoir being sealed and containing a solution of aqueous ammonia and gaseous anhydros ammonia disposed thereabove; and the output side of the pump being in communication with the reservoir at a point below the surface of the aqueous ammonia, whereby the gaseous ammonia entering the reservoir from the pump is bubbled through said aqueous ammonia to facilitate the dissolution of the aqueous ammonia and thereby generate additional quantities of anhydrous ammonia, and to raise the pressure within the reservoir above that of the developing chamber to facilitate circulation of ammonia between the reservoir and the de- Veloping chamber.

13. A developing apparatus in accordance with claim 2, in which the vacuum pump and the circulating pump Er the developing medium are both driven by a single electrical motor.

14. A developing apparatus for diazo photocopy machines comprising, in combination, a developing chamber including transport means for advancing exposed diazo-type sensitized paper therethrough; means for introducing and circulating anhydrous ammonia within the chamber to develop an image on the sensitized paper; a vacuum pump for evacuating said anhydrous ammonia from the developing chamber; and a vacuum surge chamber disposed in the line of flow from the developing chamber to the vacuum pump; said vacuum pump being adapted to pump a greater volume of anhydrous ammonia from the developing chamber than is introduced thereon to maintain the internal pressure of said developing chamber at below atmospheric to avoid external leakage of ammonia fumes; and said vacuum surge chamber being adapted to maintain said below atmospheric pressure within the developing chamber at a relatively constant level.

15. A developing apparatus in accordance with claim 14, in which the vacuum surge chamber is sealed to the atmosphere, and includes a normally closed control valve communicating the interior and exterior thereof; said valve being responsive to the below-atmospheric pressure within the surge chamber to permit the entry of ambient air when such pressure is reduced below a predetermined value.

16. A developing apparatus in accordance with claim 15, in which the valve maintains the below atmospheric pressure within the developing chamber within the range of about 0.2 inches to about 1.0 inches of water column.

17. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper through said developing chamber in the line of flow of developing medium from the inlet to the outlet, means for introducing developing medium into said developing chamber in controlled amounts via said inlet; a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber, and means connected with said developing chamber maintaining the internal pressure of said developing chamber at lower than atmospheric pressure to thereby avoid external leakage of developing medium.

l 1' I i 

1. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the oulet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium.
 2. A developing apparatus in accordance with claim 1, in which the developing chamber includes a second outlet; and said means for introducing developing medium comprises a reservoir containing developing medium; means communicating said reservoir and the inlet of the developing chamber; and a pump connected at its suction side to the second outlet of the developing chamber and connected at its output side to the reservoir to circulate developing medium between the reservoir and the developing chamber.
 3. A developing apparatus for photocopy machines compriSing, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, and a pressure sensitive control means disposed in the developing chamber and responsive to the below atmosphere internal pressure thereof to permit the entry of ambient air when such internal pressure is reduced below a predetermined value.
 4. A developing chamber in accordance with claim 3, in which said pressure sensitive means is a normally closed control valve communicating the interior and exterior of the developing chamber.
 5. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, and a vacuum surge chamber disposed in the line of flow from the outlet of the developing chamber to the inlet of the vacuum pump adapted to maintain a constant below atmosphere pressure within the developing chamber.
 6. A developing apparatus in accordance with claim 5, in which the vacuum surge chamber comprises a sealed tank having an inlet in communication with the outlet of the developing chamber; an outlet in communication with the suction side of said vacuum pump; and a normally closed control valve communicating the interior and exterior of the tank, and responsive to the below atmospheric internal pressure of said tank to open when such internal pressure is reached below a predetermined valve to permit the entry of ambient air therein.
 7. A developing apparatus in accordance with claim 6, in which the vacuum surge chamber maintains the below atmosphere pressure within the developing chamber at about 0.2 inches of water column to about 1.0 inches of water column.
 8. A developing apparatus in accordance with claim 1, in which the output of the vacuum pump is in communication with an absorption vessel containing suitable material to absorb the discharged developing medium.
 9. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developIng medium, the output of the vacuum pump being in communication with a catalytic reactor to breakdown the discharged developing medium into its non-toxic components for exhausting into the surrounding atmosphere.
 10. A developing apparatus in accordance with claim 8, in which the developing medium is anhydrous ammonia and the absorption material is citric acid.
 11. A developing apparatus in accordance with claim 9, in which the developing medium is anhydrous ammonia and the catalytic reactor breaks down such ammonia into nitrogen gas and water vapor.
 12. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper therethrough in the line of flow of developing medium from the inlet to the outlet; means for introducing developing medium into said developing chamber in controlled amounts via said inlet; and a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber; said vacuum pump being adapted to pump a greater volume of developing medium from said developing chamber than is introduced thereto, to maintain the internal pressure of said developing chamber at below atmospheric, and thereby avoid external leakage of developing medium, said developing chamber including a second outlet; and said means for introducing developing medium comprising a reservoir containing developing medium; means communicating said reservoir and the inlet of the developing chamber; and a pump connected at its suction side to the second outlet of the developing chamber and connected at its output side to the reservoir to circulate developing medium between the reservoir and the developing chamber, said developing medium being anhydrous ammonia; the reservoir being sealed and containing a solution of aqueous ammonia and gaseous anhydros ammonia disposed thereabove; and the output side of the pump being in communication with the reservoir at a point below the surface of the aqueous ammonia, whereby the gaseous ammonia entering the reservoir from the pump is bubbled through said aqueous ammonia to facilitate the dissolution of the aqueous ammonia and thereby generate additional quantities of anhydrous ammonia, and to raise the pressure within the reservoir above that of the developing chamber to facilitate circulation of ammonia between the reservoir and the developing chamber.
 13. A developing apparatus in accordance with claim 2, in which the vacuum pump and the circulating pump for the developing medium are both driven by a single electrical motor.
 14. A developing apparatus for diazo photocopy machines comprising, in combination, a developing chamber including transport means for advancing exposed diazo-type sensitized paper therethrough; means for introducing and circulating anhydrous ammonia within the chamber to develop an image on the sensitized paper; a vacuum pump for evacuating said anhydrous ammonia from the developing chamber; and a vacuum surge chamber disposed in the line of flow from the developing chamber to the vacuum pump; said vacuum pump being adapted to pump a greater volume of anhydrous ammonia from the developing chamber than is introduced thereon to maintain the internal pressure of said developing chamber at below atmospheric to avoid external leakage of ammonia fumes; and said vacuum surge chamber being adapted to maintain said below atmospheric pressure within the developing chamber at a relatively constant level.
 15. A developing apparatus in accordance with claim 14, in which the vacuum surge chamber is sealed to the atmosphere, and includes a normally closed control valve communicating the interior and exterior thereof; said valve being responsive to the below-atmospheric pressure within the surge chamber to permit the entry of ambient air when such pressure is reduced below a predetermined value.
 16. A developing apparaTus in accordance with claim 15, in which the valve maintains the below atmospheric pressure within the developing chamber within the range of about 0.2 inches to about 1.0 inches of water column.
 17. A developing apparatus for photocopy machines comprising, in combination, a developing chamber having an inlet for receiving developing medium, an outlet for discharging said developing medium, and means for transporting sensitized paper through said developing chamber in the line of flow of developing medium from the inlet to the outlet, means for introducing developing medium into said developing chamber in controlled amounts via said inlet; a vacuum pump in communication with said outlet to remove said developing medium from the developing chamber, and means connected with said developing chamber maintaining the internal pressure of said developing chamber at lower than atmospheric pressure to thereby avoid external leakage of developing medium. 